cyclic-gmp and indoleacetic-acid

The second messenger cyclic guanosine 3',5'-monophosphate (cGMP) plays an important role in plant development and responses to stress. Recent studies indicated that cGMP is a secondary signal generated in response to auxin stimulation. cGMP also mediates auxin-induced adventitious root formation in mung bean and gravitropic bending in soybean. Nonetheless, the mechanism of the participation of cGMP in auxin signalling to affect these growth and developmental processes is largely unknown. In this report we provide evidence that indole-3-acetic acid (IAA) induces cGMP accumulation in Arabidopsis roots through modulation of the guanylate cyclase activity. Application of 8-bromo-cGMP (a cell-permeable cGMP derivative) increases auxin-dependent lateral root formation, root hair development, primary root growth, and gene expression. In contrast, inhibitors of endogenous cGMP synthesis block these processes induced by auxin. Data also showed that 8-bromo-cGMP enhances auxin-induced degradation of Aux/IAA protein modulated by the SCF(TIR1) ubiquitin-proteasome pathway. Furthermore, it was found that 8-bromo-cGMP is unable to directly influence the auxin-dependent TIR1-Aux/IAA interaction as evidenced by pull-down and yeast two-hybrid assays. In addition, we provide evidence for cGMP-mediated modulation of auxin signalling through cGMP-dependent protein kinase (PKG). Our results suggest that cGMP acts as a mediator to participate in auxin signalling and may govern this process by PKG activity via its influence on auxin-regulated gene expression and auxin/IAA degradation.

Topics: Arabidopsis; Arabidopsis Proteins; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Gene Expression Regulation, Plant; Genes, Reporter; Indoleacetic Acids; Models, Biological; Mutation; Phenotype; Plant Growth Regulators; Plant Leaves; Plant Roots; Plants, Genetically Modified; Proteasome Endopeptidase Complex; Signal Transduction; Two-Hybrid System Techniques

This report describes part of the signaling pathway and some of the molecules involved in the auxin-induced adventitious root formation in cucumber (Cucumis sativus). Previous results showed that nitric oxide (NO) mediates the auxin response during adventitious root formation (Pagnussat et al., 2002). To determine the order of action of indole acetic acid (IAA) and NO within the signal transduction pathway and to elucidate the target molecules that are downstream of NO action, cucumber hypocotyl cuttings were submitted to a pretreatment leading to endogenous auxin depletion. The auxin depletion treatment provoked a 3-fold reduction of the root number in comparison to the nondepleted explants. The NO-donor sodium nitroprusside was able to promote adventitious rooting in auxin-depleted explants, whereas the specific NO scavenger cPTIO prevented the effect of sodium nitroprusside. The endogenous NO level was monitored in both control and auxin-depleted explants using a NO-specific fluorescent probe. The NO level was 3.5-fold higher in control (nondepleted) explants than in auxin-depleted ones. The exogenous application of IAA restored the NO concentration to the level found in nondepleted explants. Because NO activates the enzyme guanylate cyclase (GC), we analyzed the involvement of the messenger cGMP in the adventitious root development mediated by IAA and NO. The GC inhibitor LY83583 reduced root development induced by IAA and NO, whereas the cell-permeable cGMP derivative 8-Br-cGMP reversed this effect. The endogenous level of cGMP is regulated by both the synthesis via GC and its degradation by the phosphodiesterase activity. When assayed, the phosphodiesterase inhibitor sildenafil citrate was able to induce adventitious rooting in both nondepleted and auxin-depleted explants. Results indicate that NO operates downstream of IAA promoting adventitious root development through the GC-catalyzed synthesis of cGMP.

Topics: Cucumis sativus; Cyclic GMP; Indoleacetic Acids; Nitric Oxide; Phosphoric Diester Hydrolases; Plant Roots; Second Messenger Systems

Melatonin was given orally to patients undergoing diagnostic pneumoencephalography and various compounds were measured in the lumbar and cisternal CSF. Melatonin markedly increased plasma and CSF melatonin concentrations. The plasma: CSF melatonin ratios were similar in patients who received, and in those who did not receive, melatonin. This supports the idea that melatonin is released from pineal to blood and gets into the CSF via the blood. Melatonin did not affect CSF 5-hydroxyindoleacetic acid, which indicates that it has no effect on 5-hydroxytryptamine metabolism. Melatonin increased CSF indoleacetic acid significantly, indicating increased metabolism of tryptamine. Melatonin did not affect CSF cAMP levels, but increased cGMP levels. The effect on indoleacetic acid and cGMP was seen in both lumbar and cisternal CSF, suggesting that melatonin can have generalized actions throughout the CNS.

Topics: Adolescent; Adult; Child; Cyclic AMP; Cyclic GMP; Female; Humans; Hydroxyindoleacetic Acid; Indoleacetic Acids; Male; Melatonin; Middle Aged